The invention relates to an apparatus for the spectroscopical examination of light transmitting objects such as precious stones (gem stones) comprising a spectroscope unit, receptacle means for the object to be examined, and a light source, the object of examination in its receptacle being situated at the point of intersection of the optical axes of the spectroscope and the light source. It is the function of such devices to investigate the spectral properties or precious stones in particular, that is to say, to determine the history and nature of a gem stone by means of its line or band spectrum.
Until now spectroscopes of various kinds have been employed for this purpose, with the help of which one observes by eye a light beam that has been firstly split up by a prism and then shone through the precious stone under examination.
There are different methods and arrangements of the apparatus that can be used in the spectroscopical examination of gem stones.
It is already known (see K. Schlossmacher, "Perlen und Edelsteine," 5th edition 1969, page 97 ff) to shine light through a gem stone when examining it. For this purpose an apparatus is provided in which the light source, the gem stone and the spectroscope are arranged in that order and practically on one optical axis. The disadvantage of this apparatus is that the intensity of the spectral lines is too weak because the light path in the object under examination is too short. More advantageous is the method that is at present most commonly used, in which the principle of reflection at the upper planar surface of the gem stone under examination is used. For this purpose devices are used (see Chudoba-Guebelin, "Edelsteinkundliches Handbuch," 3rd edition 1974, page 232 ff) in which the light is shone at an angle of 45.degree. to the planar surface into the diamond, which is lying on its planar surface; the light is totally reflected and is then directed into a spectroscope, which is also angled at 45.degree. to the planar surface. The disadvantage of this arrangement is that the angle setting of the spectroscope and of the light source is not adjustable, with the result that, when one is working with differing types of gems, that is to say with different optical properties (refractive index, reflective behaviour etc.), one must always use the same optical arrangement. Apart from the fact that, when using these devices, one works with only the reflected illumination from above, the fine adjustment of the optical axes of the light source and spectroscope results in a reduction of the intensity of the spectral lines, as is the case with the known transillumination device, described above.
Finally, one more spectroscope apparatus is known (see R. T. Liddicoat jr., Handbook of Gem Identification, 9th edition 1972, page 180 ff) in which the optical axis of the spectroscope is mounted so as to be pivotable with respect to the optical axis of the light source. With this device one works with the light from a lamp that has been shone through the precious stone under examination by means of a mirror system. The disadvantage of the transillumination system, which was explained in the previous paragraph, are, however, still present, despite of the fact that the pivotability of the spectroscope enables the device to be adapted to a certain extent to the optical properties of any particular precious stone.